A method of using of a level meter employing the radar principle, serving to measure the fill level of a medium in a container and incorporating an electric conductor system for conducting an electromagnetic signal into the container and returning reflected components of the electromagnetic signal from the container, the electric conductor system terminating at a predefined level in the container. In practicing the method a variation of the component of the electromagnetic signal reflected at the container-oriented end of the conductor system is utilized as an indicator of the attainment of the predefined fill level by the medium. This permits the detection of very small amounts of a medium for instance in the monitoring of drain pipes, spillway basins or leak-detection systems.